The non-invasive technique of Laser Doppler Velocimetry provides the means whereby absolute measurements of the blood flow rate at discrete sites in the retinal vasculature may be obtained accurately and with relative ease. Measurements can be obtained in fractions of a second and changes in the velocities of red blood cells in individual retinal vessels can be followed continuously in time. Our objectives are to utilize this technique in order to (a) investigate the physiology of the human retinal circulation; especially, to quantitatively characterize the blood flow autoregulation process in the healty retina; (b) investigate the role played by alterations in retinal blood flow in the causation and development of diseases of the ocular fundus such as diabetic retinopathy, venous occlusions, and glaucoma; and (c) study the effects of systemic diseases such as diabetes, hypertension, and arteriosclerosis, and carotid artery occlusions on the retinal blood flow.